PORTSMOUTH — A fire that started in the chimney of a condominium unit on Bow Street Friday night caused more than $1 million in damage and has left at least six residences uninhabitable.

Fire crews remained on scene at 135 Bow St. throughout Saturday morning, more than 12 hours after the fire was reported.

Assistant Fire Chief Steve Achilles said multiple units sustained heavy damage as a result of the five-alarm blaze.

The fire, which was reported around 6:30 p.m., began in a masonry chimney in unit 2 of the 18-unit condo building, Achilles said. The chimney was connected to a flue, which Achilles said extended from the bottom floor to the roof.

A preliminary investigation shows it is likely the flu was damaged, which allowed the fire to breach the metal and extend into the walls.

“The fire was allowed to communicate all the way up and down the flue,” Achilles said.

The fire within the walls was fueled by foam insulation, and once it spread to the roof, firefighters had to battle a fire fueled by what Achilles said was a “rubber membrane.”

“We basically had a petroleum fire on the roof,” he said.

The roof above unit 13 eventually gave way and collapsed. Several heating, ventilation and air conditioning units also collapsed into the floors below.

While the fire caused extensive damage, Achilles said it could've been a lot worse. Had it not been for masonry fire walls located between units 12, 13 and 14, Achilles said the entire upper floor of the building would have been destroyed.

The home that sustained the most damage was unit 13, which according to city assessment records is owned by Timothy Robinson and Michaeline Daboul and is assessed at $712,000.

“Unit 13 is destroyed,” Achilles said.

Units 14 and 12 also sustained heavy smoke and structural damage, he said.

Residences on the bottom floor, units 2, 3 and 4, also sustained significant water damage, according to Achilles. All six of those units are considered uninhabitable. Units 5, 15 and 8 also sustained some water damage but were considered habitable, he said.

Achilles said because each unit is valued at more than $600,000, it is likely the fire caused in excess of $1 million in damage.

At the height of the fire Achilles said there was likely more than 100 firefighters on scene.

Firefighters and ambulance crews were called from Exeter, Rochester, Durham, Newington, Hampton, New Castle, Rye, Greenland, Pease, Dover and North Hampton, as well as Kittery and York, Maine.

The fire was challenging not only due to the cold and wind, but also because firefighters had to extend hoses hundreds of yards just to get to the blaze, Achilles said. Firefighters also had difficulty accessing the building's roof and were forced to climb through skylights.

“The challenging part was the location and the difficulty getting multiple lines in play from a remote location off the street,” Achilles said. “We also had limited access to the river side and couldn't extend a ladder to the roof.”

Overall, Achilles said it took firefighters about three hours to get the blaze under control, and crews on scene were able to contain all of the significant fire damage to only unit 13.

No firefighters or civilians were hurt

“All in all I think we were very successful given all the challenges,” he said.